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Two types of earthworm, one black and one red-brown, inhabit the woods

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#Top150 CR: Two types of earthworm, one black and one red-brown,  [#permalink]

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New post 18 Oct 2015, 19:49
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souvik101990 wrote:
Two types of earthworm, one black and one red-brown, inhabit the woods near the town of Millerton. Because the red-brown worm's coloring affords it better camouflage from predatory birds, its population in 1980 was approximately five times that of the black worm. In 1990, a factory was built in Millerton and emissions from the factory blackened much of the woods. The population of black earthworms is now almost equal to that of the red-brown earthworm, a result, say local ecologists, solely stemming from the blackening of the woods.

Which of the following, if true, would most strengthen the conclusion of the local ecologists?

A. The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.

B. The birds that prey on earthworms prefer black worms to red-brown worms.

C. Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.

D. The average life span of the earthworms has remained the same since the factory began operations.

E. Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.


Causality!
Given: Woods blacken because of factory's emission (cause) => Red-brown worms lost the camouflage advantage and are preyed upon more. (effect)
We need to strengthen this.

General theory regarding causal arguments- Implicit assumptions by the author:
1) Cause happens before the effect
2) Effect does not cause the cause
3) There is no alternate cause for the effect (the stated cause is the only cause)
Any of the above 3 will strengthen the argument.

Answer choice C helps in establishing assumption 3 above. It discards one of the possible alternate causes for decreasing population of red-brown worms- Adverse climate conditions.
C. Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.

Therefore, this is a clear strengthener.

Hope this makes sense :)
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Re: #Top150 CR: Two types of earthworm, one black and one red-brown,  [#permalink]

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New post 21 Dec 2015, 05:11
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Hello Souvik

Can you please provide the solution/OE - I am still confused between B and C.

Thank you
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Re: #Top150 CR: Two types of earthworm, one black and one red-brown,  [#permalink]

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New post 27 Dec 2015, 22:26
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Any answer choice which says that the population of black earthworm increased because of factory emissions is my answer. "B" suggests that though birds prefer black earthworms to red ones it necessarily does not suggest that these birds ate more black earthworms than reds."E" weakens the ecologists'contention. If factory emissions reduces then the population of black earthworm should have decreased and not increased because these no longer were camouflaged.In "C" climatic conditions did change because of the emissions. So maybe the new climatic conditions were favorable for the Black worms. Hence "C" is the answer.
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Re: Two types of earthworm, one black and one red-brown, inhabit the woods  [#permalink]

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New post 19 Apr 2016, 04:11
Logic of GMAC is:
Before Event X: A was LESS than B.
After Event X: A equals B. OR A is larger than B.
Conclusion: X must cause A increase.
Assumption is: No factors make B decrease
I think that after the event X,A did not increase but B decreased due to predation so how can the conclusion be X must cause A increase ( although A might have increased through reproduction) At some point both A and B became equal
Can anyone please clarify!?

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Re: Two types of earthworm, one black and one red-brown, inhabit the woods  [#permalink]

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New post 19 Apr 2016, 11:03
shivakumarmakka wrote:
Logic of GMAC is:
Before Event X: A was LESS than B.
After Event X: A equals B. OR A is larger than B.
Conclusion: X must cause A increase.
Assumption is: No factors make B decrease
I think that after the event X,A did not increase but B decreased due to predation so how can the conclusion be X must cause A increase ( although A might have increased through reproduction) At some point both A and B became equal
Can anyone please clarify!?

Dear shivakumarmakka
I'm happy to respond. :-)

Let's say
A = black earthworm population
B = red-brown earthworm population

Before event, A < B. Technically, A = 5B, approximately.

BUT, be careful. After event, it does not say A > B or even A = B. The exact wording is
"The population of black earthworms is now almost equal to that of the red-brown earthworm ..."
Technically, A is still less than B: now, not five times less, but just slightly less. It's misreading the question to say that A is greater than B.

Also, notice that nowhere in the question itself does it suggest that the black worms have increased. The prompt argument doesn't even contain the word "increase." In fact, the question is about B decreasing. The factory has blackened the woods, and presumably the black worms are now well camouflaged, but the red-brown worms are easier to spot, so the birds snack on these. We don't know whether the black worms have stayed the same or increases, but through some combination of B dropping and A staying the same or rising, A has almost caught up to B.

My friend, you have to remember that GMAT CR is as precise as mathematics. You have to look at every single word incredibly carefully. It appears you got the gist of the argument and concluded in your own mind that it was saying things different from what it actually says. Be very careful. As in any argument in the business world, the fine print matters, and many business deals that look great on the surface turn out to be nightmares when you examine the details.

Does all this make sense?
Mike :-)
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Re: #Top150 CR: Two types of earthworm, one black and one red-brown,  [#permalink]

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New post 02 Jun 2018, 05:15
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souvik101990 wrote:
Two types of earthworm, one black and one red-brown, inhabit the woods near the town of Millerton. Because the red-brown worm's coloring affords it better camouflage from predatory birds, its population in 1980 was approximately five times that of the black worm. In 1990, a factory was built in Millerton and emissions from the factory blackened much of the woods. The population of black earthworms is now almost equal to that of the red-brown earthworm, a result, say local ecologists, solely stemming from the blackening of the woods.

Which of the following, if true, would most strengthen the conclusion of the local ecologists?

A. The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.

B. The birds that prey on earthworms prefer black worms to red-brown worms.

C. Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.

D. The average life span of the earthworms has remained the same since the factory began operations.

E. Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.


VERITAS PREP OFFICIAL SOLUTION:



Correct Answer: C

The argument concludes that the change in coloration of the woods has been the sole cause of the change in the earthworm population. To strengthen the conclusion that the coloration was the sole cause of the improved status of the black earthworms, eliminate other possible causes. Choice C says that the change was not about the climate, which favored the red-browns, making it the correct answer. Choice A allows for the possibility that the equal number of worms was because of a drop in the red-browns, not an increase in the blacks, which might weaken the conclusion. Ultimately, though, it doesn't tell us why the red-browns dropped, so it doesn't really have any effect. For answer choice B, what the birds prefer is irrelevant; the argument is about what they actually eat. Answer D provides us no way to distinguish between the two types of worms. While E may be good to know, it does not strengthen the conclusion.
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Re: #Top150 CR: Two types of earthworm, one black and one red-brown,  [#permalink]

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New post 02 Oct 2018, 20:20
Comprehension gap:

Should it be considered, the black worms' population is increasing due to blackened woods or red worms' population decreased due to blackened woods. I went with the later one and hence chose A.

#toughie

Choosing the wrong one among the last two, mostly
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Two types of earthworm, one black and one red-brown, inhabit the woods  [#permalink]

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New post 22 Oct 2018, 14:56
TGC wrote:
Two types of earthworm, one black and one red-brown, inhabit the woods near the town of Millerton. Because the red-brown worm's coloring affords it better camouflage from predatory birds, its population in 1980 was approximately five times that of the black worm. In 1990, a factory was built in Millerton and emissions from the factory blackened much of the woods. The population of black earthworms is now almost equal to that of the red-brown earthworm, a result, say local ecologists, solely stemming from the blackening of the woods.

Which of the following, if true, would most strengthen the conclusion of the local ecologists?


A. The number of red-brown earthworms in the Millerton woods has steadily dropped since the factory began operations.

B. The birds that prey on earthworms prefer black worms to red-brown worms.

C. Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.

D. The average life span of the earthworms has remained the same since the factory began operations.

E. Since the factory took steps to reduce emissions six months ago, there has been a slight increase in the earthworm population.


What is wrong with option (A)? As we have to prove that after factory operations the red ones were more visible than the black ones ,so this should provide support to "Black = Red solely stemming from the" blackening of the woods."
Knowing that factory operations was the cause of " blackening of the woods."



okay here is my reasoning why i chose C

Since, in 1990, a factory was built in Millerton and emissions from the factory blackened much of the woods.

The population of black earthworms is now almost equal to that of the red-brown earthworm, i.e. the population of black worms increased and the population of brown worms stagnated

Local ecologists say it is the blackening of the woods.

Ecologists`s claim implies that emissions enabled black worms to use their color as a comouflage.

To strengthen this claim one need to find a factor that could have negative affect on black worms. so based on option (C) despite favourble conditions for the red brown worm, its population didn`t grow whereas for black worm though climate conditions were less favourable, their black camouflage gave them opprtunity for survival and growth in black woods. hence C :)

Climate conditions since 1990 have been more favorable to the survival of the red-brown worm than to the black worm.
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Re: Two types of earthworm, one black and one red-brown, inhabit the woods  [#permalink]

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New post 14 May 2019, 09:42
A and B are good answers, but C is better.

A strengthens the argument because it says the red worm population is falling. One possible explanation is the black worms are now better camouflaged so the birds are eating more red worms.

But A isn’t ideal because there are other plausible explanations. Maybe there is a disease that’s killing red worms. We don’t know. A is tempting us to assume that the blackening of the forest is why the red worm population is falling but we don’t really know that for sure. So maybe this fact strengthens, or maybe it’s just a coincidence.

B is good, too, but it isn’t perfect. It says birds prefer black worms so you you would expect them to eat more black worms. Yet, the black worm population is rising. So we’re tempted to assume the birds would rather eat black worms but they aren’t doing so because the black worms aren’t visible so the birds settle for eating red. Okay, maybe. Or maybe the birds are still eating tons of black worms. We know the population of red and black is now equal but we don’t know that there are more black worms. Maybe they’re equal entirely because the population of red worms fell. Is that because the birds can see the red worms and are eating more of them? That’s a fair supposition but maybe something else, like disease or climate change, is causing the red worm population to fall.

And that takes us to C. C is best because it is ruling out these alternative explanations. A and B are plausible explanations, but they leave other possibilities open. C forecloses those possibilities.

This one is really hard, I would not fault anyone for picking A or B. We see a lot of questions where all the answers are bad and we have to find the least bad. Here, we have to pick the best of three pretty good answers.

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Re: Two types of earthworm, one black and one red-brown, inhabit the woods   [#permalink] 14 May 2019, 09:42

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